1. Field of the Invention
This invention relates generally to conveyors for feeding logs into a sawmill or other log processing machines and more particularly to an infeed conveyor having laterally adjustable flights and cooperative adjustment mechanism for angularly and laterally repositioning logs for optimum recovery during the infeed process.
2. Description of the Prior Art
As the cost of lumber has increased, it has become increasingly necessary to optimize lumber recovery from logs of varying sizes and shapes. In addition, economics dictates that such recovery be performed in a highly efficient operation with a large volume output. Therefore, to obtain optimum recovery of useful lumber at relatively high efficiencies, log processing must, to some extent, be automated.
It has previously been recognized that optimum yield of useful lumber cannot always be achieved by sawing a tapered log along its centerline. By "taper sawing", "offset-center sawing" or "offset-taper sawing" irregularly shaped logs, lumber recovery can be improved. Blickenderfer, et al, U.S. Pat. No. 3,519,045, recognize the advantage of aligning a log for sawing along lines other than the centerline of the log. To perform such alignment, Blickenderfer employs a log alignment structure separate from and alongside an infeed conveyor. Logs are received and aligned on this structure and then transferred to the conveyor for infeeding into a log processing stage. Although the Blickenderfer apparatus appears capable of meeting the speed requirements of a modern, high-efficiency lumber mill, it does so with considerable complexity and expense in the alignment apparatus. It would be preferable to use the infeed conveyor itself to align the logs as they move along the conveyor, and thereby meet the speed and efficiency requirements of a modern sawmill while minimizing the cost and complexity of alignment machinery.
Several devices have been used for percentering logs on a conveyor for processing, but they are not useful for deliberately off-setting a log laterally or angularly with respect to a conveyor. Hahn, U.S. Pat. No. 503,908, discloses a cable-mounted flight wherein a log is centered between V-shaped members of such a flight, but such flight has no lateral adjustment means. Nilsson U.S. Pat. No. 3,608,700, discloses a log conveyor with laterally-movable log grippers and a V-shaped groove longitudinally disposed along the centerline of the conveyor, but such grippers and grooves are not laterally adjustable for orientation of a log either angularly or laterally on the conveyor.
Tannerstal, U.S. Pat. No. 3,319,773, and McLeod, U.S. Pat. No. 3,356,205, both disclose V-shaped log conveyors intended to center a log for sawing, but neither device discloses any lateral adjustment feature.
Noriyuki, et al, U.S. Pat. No. 3,895,662, and Reed, U.S. Pat. No. 3,664,395, disclose log precentering devices for veneer lathes, both employing V-shaped blocks for holding a log, but in neither device are such blocks used in connection with a log conveyor.
Andersson, et al, U.S. Pat. No. 3,858,631, discloses a device for centering logs in a fixed position between a rollertype conveyor system and a sawing stage, rather than moving integrally with a chain-type conveyor.
Three devices disclose means for laterally or angularly positioning a log in an infeed conveyor system but none of them meets present sawmill requirements. Lynch, U.S. Pat. No. 343,328, shows a longitudinally static log trough used to position logs for entry into a sawing stage. The trough comprises two V's longitudinally disposed above a conveyor. Each such V is adjusted laterally to position a log held thereon so that one side of the log substantially parallels the conveyor. Once positioned, the log, which has been stationary in the trough while being laterally positioned, is engaged by dogs on the conveyor and carried into the slabbing machine, the trough remaining in position.
However, Lynch's design is too inefficient for use in a modern lumber mill. Time is lost placing a log in the trough and aligning it before it resumes its journey to the next stage. Then the conveyor must remove the aligned log from the trough before the trough can receive a succeeding log, resulting in further time loss.
Ackerfeldt, U.S. Pat. No. 3,665,984, shows a log-positioning system wherein three gripping devices are used to position curved logs on a conveyor for cutting. The gripping device nearest the cutting machine remains longitudinally static while the other two gripping devices are longitudinally adjustable to the length of the log in process. All three gripping devices are transversely movable on overhead frames above the conveyor. Each gripping device uses a pair of downwardly extending arms which cooperate to grasp a log and hold it while the carriages traverse the overhead frame positioning the log. Once the log is positioned, the gripping arms release it onto the conveyor to be carried into the sawing stage. Again, time is lost during the alignment of a log. In addition, Ackerfeldt's invention lacks means for holding a log in position, once aligned, securely enough to resist the lateral forces of some lumber processing machines, such as chipping edgers.
Grant, U.S. Pat. No. 1,804,764, discloses a log-bearing, track-mounted carriage having log bearing head blocks which are movable transversely of the carriage, but not while the carriage is moving.
All of the above devices have the common failing of requiring an interruption in the infeed travel of a log in order to reposition it for optimum lumber recovery, thereby making lumber production slower than it might otherwise be should it be possible to reposition the log as it moves on an infeed conveyor toward the log-processing machinery.